An analytical model of subtropical mode water is presented, based on ventilated thermocline
theory and on numerical solutions of a planetary geostrophic basin model. In ventilated
thermocline theory, the western pool is a region bounded on the east by subsurface
streamlines that outcrop at the western edge of the interior, and in which additional dynamical
assumptions are necessary to complete the solution. Solutions for the western pool were
originally obtained under the assumption that the potential vorticity of the subsurface layer
was homogenized. In the present theory, it is instead assumed that all of the water in the pool
region is ventilated, and therefore that all the Sverdrup transport is carried in the uppermost,
outcropping layer. The result is the formation of a deep, vertically homogeneous, fluid layer
in the northwest corner of the subtropical gyre that extends from the surface to the base of
the ventilated thermocline. This ventilated pool is an analog of the observed subtropical mode
waters. The pool also has the interesting properties that it determines its own boundaries and
affects the global potential vorticity-pressure relationship. When there are multiple outcropping
layers, ventilated pool fluid is subducted to form a set of nested annuli in ventilated,
subsurface layers, which are the deepest subducted layers in the ventilated thermocline.

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The Western Waters Digital Library (WWDL) provides free public access to digital collections of significant primary and secondary resources on water in the western United States. These collections have been made available by research libraries belonging to the Greater Western Library Alliance (GWLA) and other academic library partners. The WWDL is a valuable resource for researchers, policy makers, scholars, Native American tribes, professionals working in various fields, and others interested in contemporary and historic water issues.